History and Importance of Microbiology

1. Describe how the experiments both Redi and Pasteur conducted helped

disprove the idea of spontaneous generation.

How is it that these experiments allowed people to understand that life comes

from other living organisms, not just when environmental conditions are right? (1

point)

Answer:

The theory of Spontaneous Generation supported the fact that life could be

spontaneously generated from the non living matter.

In the 17th century, an Italian scientist Franceso Redi conducted an experiment

to controvert the theory of Spontaneous Generation. He showed that fly larvae do

not spontaneously arise from decaying meat.

1. He placed meat in two identical jars and left one jar uncovered and allowed

flies to come into contact with the meat. He covered the other jar with a cheese

cloth that allowed air to pass through. Contact with the air allowed the meat to

decay.

2. After a short period of time, he observed fly larvae on the decaying meat of the

open jar. There were no fly larvae on the meat in the covered jar.

3. Redi concluded that the flies laid eggs on the meat in the open jar. As the flies

had not laid eggs on the meat in the covered jar, no fly larvae were produced.

Thus, Redi therefore proved that decaying meat did not produce fly larvae.

In the late 1800s by Louis Pasteur concluded same theory with a classic

experiment. His hypothesis states that if cells could arise from nonliving

substances, then they should appear spontaneously in sterile broth.

To test his hypothesis, he created two treatment groups:

a) One broth that was exposed to a source of microbial cells.

b) One broth that was not exposed to a source of microbial cells.

For control treatment, he used a straight-necked flask that allowed particles in

the air to fall into the broth stored in the flask. For his experimental treatment,

Pasteur used a swan-necked flask. The neck shaped and length assured that no

cells could enter the broth from the air.

Pasteur then performed the same procedure on these two flasks. He boiled the

broth to kill any existing organisms. He then let the broth cool and allowed it to

sit for several days, after which he removed the necks of the flasks and checked

the broth for the growth of any organisms. Pasteur found living organisms only in

the control flask. Because the experimental flask remained sterile, the hypothesis

of spontaneous generation was rejected.

2. Why is cell theory an important part of microbiology and how does it contribute

to the field still today? (1 point)

Answer:

The Cell Theory supports the idea that cells are the basic unit of structure in

every living thing. It was proposed by german scientists Theodor Schwann,

Matthias Schleiden and Rudolph Virchow. The cell theory is one of the basic

foundations of life science.

The Cell Theory states that:

· All living organisms are composed of cells. They may be unicellular or

multicellular.

· The cell is the basic unit of structure and function in all living

organisms. Existing cells arise from pre-existing cells.

· Energy flow (metabolism and biochemistry)occurs within cells.

· Heredity information (DNA and RNA) is passed on from cell to cell.

· All cells are basically the same in chemical composition in organisms of

similar species.

3. Describe how Koch’s postulates relate to the germ theory of disease and how it

is his series of experiments/steps help us link certain microbes to certain

illnesses. (1 point)

Answer:

Robert Koch was the first scientist to devise a series of tests used to assess the

germ theory of disease. Koch's work published in 1890 and demonstrated that

anthrax was caused by the bacterium Bacillus anthracis. These postulates are still

used today to help determine whether a newly discovered disease is caused by a

microorganism.

4. Discuss the three main categories of microbial control we went over during

lecture. Provide at least one example for each broad category and tell me how

that practice influenced human health/disease. (1point)

Answer:

1. Protozoa are single-celled eukaryotic organisms, exist in both water and soil.

Most protozoa feed on bacteria and decaying organic matter, although a wide

range of protozoan species are insect parasites. The protozan Nosema locustae is

a natural bio control agent of many grasshopper species. Nosema infects at least

90 species of grasshoppers. It is non-toxic to humans and other mammals.

2. Trichoderma species. are the most common fungi in nature, act as bio control

agents. These microbial bio fungicides out-compete pathogenic fungi for food and

space, and in the process can stimulate plant host defenses and affect root

growth. They also have the ability to attack and parasitize plant pathogens under

certain environmental conditions

5. Go to one of the links I provided in the “Extra Resources” section of the

PowerPoint. Look it over, play a game, etc. and tell me what your experience

with it was and why it could be useful in your life either personally or

professionally. Make sure to provide me with the link you used and a brief

description of what you did while on that site. (1 point)

Structure and Function of Prokaryotic Cells

1. Starting from the outside and working in (or vice versa) describe the

generalized prokaryotic cell. List the major structures in the cell and provide a

brief piece about their functions as well. Why is it that knowing about the

structure and function of these types of organisms is so important? (2 points)

Answer:

Prokaryotic Cell Structure

Prokaryotic cells do not have true nucleus as the DNA is coiled up in a region of

the cytoplasm known as nucleoid. The major structures of prokaryotic cells are:

a) Capsule: It is found in some bacterial cells. It provides an additional outer

covering protects the cell when it is engulfed by other organisms, helps in

retaining moisture. capsule also assists the cell adhere to surfaces and nutrients.

b) Cell Wall: It is the outer covering(in most of the cells), that protects the

bacterial cell and provides a shape to it.

c) Cytoplasm: It is a gel like substance composed mainly of water. It also

contains enzymes, salts, cell components and other organic molecules.

d) Cell Membrane: It surrounds the cell's cytoplasm and regulates the in and

out flow of substances in the cell.

e) Pili: It is a hair-like structures on the surface of the cell. It helps cell to attach

to other bacterial cells. Shorter pili is known as fimbriae.

f) Flagella: Flagella is a long, whip-like protrusion that helps in cellular

locomotion.

g) Ribosomes: Ribosomes are responsible for protein production.

h) Plasmids: Plasmids are the circular DNA structures carrying genes on them.

They are not involved in reproduction.

i) Nucleiod: Nucleid is the area of the cytoplasm that contains the single

bacterial DNA molecule.

2. Describe the main differences between Gram positive and Gram negative

bacterial cells. What are the basic steps in the staining process and how do they

work to allow us to differentiate between a Gram positive and Gram negative cell.

If you want to draw the structures to help you illustrate your points, feel free. (2

points)

Answer:

Gram positive bacteria retain a crystal violet dye during the Gram staining

process. They appear blue or violet under a microscope, whereas Gram-

negative bacteria appear red or pink. This difference in classification is due to

difference in the cell wall of the bacteria.

Major characteristics of Gram-positive bacteria are:

1. They have a thick cell wall made of peptidoglycan.

2. If a flagellum is present in them, it contains two rings for support.

3. Teichoic acids are present in gram positive bacteria. It act as chelating

agents and assist bacteria for adherence.

Gram negative bacteria are those that do not retain crystal violet dye. They are

mostly pathogenic. Major characteristics of Gram-negative bacteria are:

1. Cell walls contain a few layers of peptidoglycan and surrounded by an

outer membrane of lipopolysaccharide

2. outside the peptidoglycan layer.

3. Porins exist in the outer membrane.There is a space between the layers of

peptidoglycan and the secondary cell membrane. This space is known as

the periplasmic space.

4. If flagella is present, it has four supporting rings instead of two.

5. No teichoic acids are present

6. Lipoproteins are attached to the polysaccharide backbone whereas in

Gram-positive bacteria no lipoproteins are present.

Gram Staining technique:

Prepare a light suspension of cells from very young cultures grown on appropriate

agar medium. If the suspension prepared is too turbid, dilute with distilled water.

1. Add one drop to a clean glass slide and spread the drop with a loop over

the surface of the slide. Allow to air-dry.

2. Fixate the cells by moving the slide into a flame .

3. Flood the slide for 1 minute with Hucker's reagent. and then wash it by

dipping the slide into slow running tap water.

4. Flood the slide with iodine solution for 1 minute and then place it

diagonally in glass box and rinse of iodine solution with safranin.

5. Add excess amount of fresh safranin and wait for 35 seconds, then rinse

slide with water and allow the slide to air-dry.

6. Examine the slides in the microscope. A drop of oil can be placed on the

slide directly.

7. Gram-positive cells appear purple and Gram-negative cells pink.

3. Pick at least one of the special structures we discussed (fimbriae, flagella or

endospores) and discuss why this structure can be useful for the bacterium. Tell

me why knowing about this structure is important for us as well. (1 point)

Answer:

Certain bacteria form endospores in dry environments. This process of endospore

is known as sporulation. They are also known as endospores, because the spores

are formed within the cell. Endospores are very advantageous to bacterial cells.

They are extremely resistant to a number of harsh environments, such as heat,

desiccation, radiation, chemicals, acids, and drying.

Bacillus subtilis spores proved to be useful for the expression of recombinant

proteins. Particularly for the surface display of peptides and proteins , which act

as a tool for fundamental research in the fields of biotechnology and vaccination.

Structure and Function of Eukaryotic Cells

1. Again, starting from the outside in (or vice versa) describe the generalized

eukaryotic cell (make sure to mention both the cell-walled and non-cell-walled

varieties). List the major structures in the cell and provide a brief piece about

their functions as well. Why is it that knowing about the structure and function of

these types of organisms is so important? (2 points)

Answer:

Eukaryotic cells have an organized nucleus with a well developed nuclear

envelope. The nucleus is known as the brain for the cell. This is the discrete area

to keep DNA. Such well developed nucleus is known as true nucleus. Eukaryotic

cells are mainly classified in two categories:

a) Plant cells

b) Animal Cells

In animal cells , cell wall is absent whereas in plant cells cell wall is present. The

major structures of plant and animal cells are listed with their functions. The

major structures of plant and animal cells are listed with their functions:

Cell Organelles Functions Animal Cell Plant Cell

Nucleus Genetic information

is stored

Present Present

Cilia Responsible for

movement

Present rare

Chloroplast Photosynthesis Animal cells don't

have chloroplasts

Plant cells have

chloroplasts

because they make

their own food

Endoplasmic

Reticulum ,

Golgi

Apparatus and

Ribosomes

Protein synthesis Present Present

Mitochondria ATP production

known as

powerhouse of cell

Present Present

Cell wall Provides protection

and rigidity

Absent Present

Flagella Locomotion May be found in some

cells

May be found in

some cells

2. Discuss endosymbiotic theory. Tell me how it works, what the evidence for it

is, and why it is important to understand. (1 point)

Answer:

According to this theory, certain organelles originated as free-living bacteria that

were taken inside another cell as endosymbionts.The theory supported that:

1. Mitochondria are the result of endocytosis of aerobic bacteria.

2. Chloroplasts are the result of endocytosis of photosynthetic bacteria.

Symbiosis occurs when two different species benefit one another. When an

organism actually lives inside the other it's called endosymbiosis. The

endosymbiotic theory describes how a large host cell and ingested bacteria could

easily become dependent on one another for survival, resulting in a permanent

relationship.

3. Compare and contrast prokaryotic and eukaryotic ribosomes. Why is the

difference in ribosomes so important for us to understand? How can we use

these differences to our advantage? (1 point)

Answer:

In eukaryotes ribosomes are either free in the cytoplasm. Sometimes, they are

attached to the outer membrane of endoplasmic reticulum through ribophorins

and 60s larger subunits. In the cytoplasm of eukaryotes 80s ribosomes. The two

subunits are 60s type and 40s type. Eukaryotes also have 70s ribosomes in

mitochondria and chloroplast.

In prokaryotes the ribosomes are only in free form in the cytoplasm. It is of 70s

type in prokaryotes and divided in two subunits as 50s and 30s. Eukaryotic

ribosomes are much larger then prokaryotic ribosomes.

4. List and briefly describe the characteristics of the four types of eukaryotes of

medical significance. Provide at least one way each type of eukaryote affects

human health. (2 points)

Answer:

Virus is the most common eukaryotic organism employed in the attenuated

vaccines. Attenuated vaccines are created by keeping alive and reducing the

virulence of a pathogen. By the process of attenuation, an infectious agent

becomes harmless and less virulent. Toxoid vaccines are made from inactivated

toxic compounds that cause illness rather than the micro-organism. Examples of

toxoid-based vaccines are tetanus and diphtheria.

1. Oral polio vaccine (OPV) is a live-attenuated vaccine, produced by the passage

of the virus through non-human cells

2. The measles-mumps-rubella-varicella combo i.e MMRV vaccine is consist

attenuated live measles(genus Morbillivirus) virus.

3. Ty21a is a live typhoid vaccine made from Ty2 Salmonella Typhi strain

4. Bacillus Calmette Guerin is a vaccine against tuberculosis that is prepared from

a strain of the attenuated live bovine tuberculosis bacillus, (Mycobacterium

bovis).

1. What is the basic structure of a virus? How do each of those structures play a

role in disease? (1 point)

Answer:

Virus consist a nucleic acid surrounded by a protective coat of protein called a

capsid. They are enclosed in an envelope made of lipid, which is derived from the

host cell membrane. The capsid is made from proteins encoded by the viral

genome . Th shape of capsid serves as the basis for morphological distinction.

Viral have two major elements:

a) A DNA or RNA genome

b) A protein coat or capsid. The capsid is further classified in two major

categories:

i) A helical form, where proteins form a cylindrical tube around the genome.

ii) A Icosohedral form, where genome is compacted within a 20-sided complex of

proteins.

Some viruses such as bacterial T-phages, have a contractile sheath that can act

as a syringe and numerous tail fibers to assist in attaching to the cell wall play

important role in infecting the host.

Answer:

HIV and other retroviruses are enveloped. They have a capsid is surrounded by a

phospholipid membrane, which is derived from the host cell.

2. List and describe the steps of a viral infection. What happens during each of

the stages? (2 points)

Answer:

Virus infect host cells in two stages:attachment and penetration.

Viruses attach itself to the host cells by way of cellular receptors..

Stages of viral infection and replication are:

1. Viruses attach itself to the host cells by way of cellular receptors. A cell

cannot be infected unless it expresses the molecule that serves as a

receptor for that particular virus on its outer surface.

2. Virus injects its genome into host cell. Viral genome starts replication

using the host's cellular machinery.

3. After replication all viral components and enzymes are produced and

assembled in the host cell.

4. After maturation, newly produced viruses are released from the host cell

and start attaching to other cells.

3. Why are bacteriophages so important in human health if they can only infect

bacteria? If this type of virus can’t attach to and infect a human cell, why do

these types of viruses matter to us? (1 point)

Answer:

They prey only on bacteria, never on human cells or those of any more complex

organism. Bacteriophages act a therapeutic agent. They are naturally occurring

viruses that can infect and kill bacteria. The bacteriophages are found in human

and animal intestines.

Even among their bacterial hosts, bacteriophages are highly specific, with most

infecting only a single species of bacteria. In many cases, only specific strains

within that species are infected.

Bacteriophage infection is of two types:

a) Lytic: The bacteriophage infect the host cell, reprogram and then destroying

the infected cell.

b) Lysogenic: The bacteriophage genome is integrated into the bacterial genome

and passed on to future generations of bacteria.

Bacteriophages are important because they can be used as therapeutic agents

against harmful bacteria.

4. What are some of the ways viruses can be helpful to humans? You can use the

examples we discussed n class or go do some of your own research. Make sure

to include a website or a reference if you look for your own examples so I can

look it over too. (1 point)

Answer:

Viruses, sometimes prove to be very helpful to humans. For example, Lytic

bacteriophages are the type used for therapeutic agents. As, it will produce

hundreds of new bacteriophages from an infected bacterial cell in a matter of

hours and destroy more of the target bacteria. They are target specific. Without

their target, they are simply small lumps of protein and nucleic acid which can be

removed by the normal clearance processes of the body.

References :

1. Varnam A. H, Evans M. G., 2000. Environmental microbiology. Manson

Publishing.

2. Brock T. D. , 1999. Milestones in microbiology. ASM Press.

3. Durieux A., Simon J.P, 2001. Applied microbiology. Springer.

4. Glazer A. N., Nikaid H., 2007. Microbial biotechnology: fundamentals of

applied microbiology.Cambridge University Press.

5. Laskin A. I., Gadd G.M., Sariaslani S., 2011, Advances in Applied

Microbiology. Academic Press.